accelerated ageing tests which can only provide a rough estimate of longevity. Media technology also evolves quickly. New media types supercede older media and the devices needed to read a particular kind of media are often discontinued far sooner than the media physcially degrades. It is therefore important to have a comprehensive strategy in place for ensuring that the bitstreams of digital objects are stored on suitable media at all times and are checked on a regular basis. The following elements should all form part of a physical preservation strategy for digital media: